Thank you very much XW5. I think I will keep my own site in mind for future but for now I think I will just try and have some decent photographs taken for some of the directories - hopefully this will be enough for now!
Annabella
For higher rates and outcalls and things, you really do need to focus on building a "brand" for yourself, which includes stuff like blogging, tweeting and keeping your site consistently updated with new and interesting content. None of that is essential - there are lots of successful escorts who don't do all of them - but they really do help.
You can get yourself a blog (Wordpress.com, Blogger.com et al) & Twitter account for free in about two minutes tops so if time or money are your concern, then you're worrying needlessly. Also, if you're concerned about getting ripped off or having to have an unprofessional-looking site, talk to xw5 for answers to that!
The main directories that I know of that create a full profile for you are Adultwork and Cherrygirls. Lots of people only use AW (you can blog on there if you don't mind their draconian rules and persistent refusal to respond to help requests with anything but template auto-responses) but then you are at that site's mercy so if it goes down, you lose your entire source of income. That might not matter when you're established and have regulars, but when you're new and if you're not doing much else to stand out above the competition, it could be much worse.
I found Cherrygirls to be absolutely useless for anything but obvious timewaster callers, and the owner tried to solicit me into joining a special "agency" wherein he would pimp me out to any random guy who paid a subscription to another site he ran and I'd then have to provide Mr Random with a discount, so I unfortunately can't personally recommend them. You need to charge ?350+ to even get into the "high class" section of their site, and you need to pay hundreds per month if you want to be shown in any additional sections like "blonde" or "student" or whatever. But again, I think others have had some success - I'm just not sure if it would be worth it if you're planning to be part-time.
So really, xw5's advice makes the most sense overall because having control over your own marketing is
extremely important in this business. Leaving the promotion of yourself to others is never going to be as effective as doing it yourself. And if you're looking to make a good independent living, you want to appeal to a broad client base, so ruling out getting a website (when they can be free, or almost-free + effort-free) limits yourself unnecessarily.
I think all of us prossie-bloggers have stories about lots of clients who said they made their appointment based on something they've read that we've written - as well as our pictures, of course!

It really is a good way to reach out to them and let them know who you are and what you can offer them beyond the usual "I'm a sensual beautiful educated classy companion" profile text.